Officers were on patrol at about 11pm last night when they noticed the smell of the drug while in Fordham Road. They followed the scent to an industrial unit in Regal Drive.

Police forced entry to the premises and discovered thousands of cannabis plants with a estimated potential street value yield of up to £6million.

A police spokesman said: “There were two people living at the factory in squalid conditions. When we tried to break the door down one of them jumped from a first-floor window (to evade arrest).

“We caught one of them with the help of a dog unit, but the other person remains at large.”

The man, who is believed to be from Vietnam, was arrested on suspicion of producing cannabis and taken to Parkside Police Station, in Cambridge. He was later bailed to return to Parkside on July 24.

Inside the factory, police found plants at various stages of production and a compost heap from cultivated plants. Dozens of bags of fertiliser were also discovered.

The police spokesman estimated that the factory has been running for about a year and the potential street value of the plants discovered is up to £6m.

Scenes of crime officers carried out investigations at the site today to establish how many plants are in the unit. They are due to return tomorrow.

Sgt Dan Bramley said: “This was good proactive work by the officers who tracked down the cannabis factory after noticing the smell.”

If police predictions about the value of the plants are correct, it will be the largest cannabis factory ever discovered in Cambridgeshire.

The largest ever discovered was a factory at Tree Farm, in Haddenham, which was raided by police in 2010. The estimated street value of the recovered plants was £1.75million, with a yearly yield of about £8million.

In October last year, Kevin Hart, of Elm Close, Huntingdon, the main who managed the Haddenham factory, was jailed for 10 years for conspiring to produce cannabis. He was also ordered to pay back more than £1million after conceding to a criminal benefit of £8.5million.

The owner of the land and barn, Neil Badcock, of Linden Way, Haddenham, was also jailed for seven years after he was found guilty of conspiracy to produce cannabis after a trial.

Six other people, from the Huntingdonshire area, were jailed for a total of almost 20 years for conspiracy to produce cannabis.